The present invention relates to a manufacturing method of a semiconductor device which comprises the steps of forming a copper-containing film, and more particularly to a manufacturing method of a semiconductor device having an interconnection, an interconnection connecting plug, a pad section or such, made of copper or a copper alloy.
In recent years, copper and copper alloys have been widely used as the material for interconnections and connecting plugs to achieve higher speed operations in the elements. With these metals utilized, the interconnections and the likes are generally formed by the damascene method.
FIG. 5 is a series of views illustrating the steps of a conventional method of forming a copper interconnection. Now, this method is described below. First, as shown in FIG. 5(a), after an insulating film 10 and an interlayer insulating film 12 are formed, in this order, on a semiconductor substrate (not shown in the drawings), an interconnection trench is set within the interlayer insulating film 12, and thereon a barrier metal film 14 made of Ta; TaN or such and a seed copper film 15 are formed, in succession, and then a copper film 16 is formed by the plating method.
The semiconductor wafer 1 in this state is subjected to the chemical mechanical polishing (CMP) and copper lying outside of the interconnection trench is removed, while copper lying inside of the trench is left as it is, whereby a copper interconnection 17 is formed. At this, copper oxide 21 is produced on the copper interconnection 17, and a carboxylic acid cleaning is performed (FIG. 5(b)) for removing this copper oxide 21. In this way, copper oxide which may cause an increase in interconnection resistance or contact resistance can be eliminated (FIG. 5(c)). After that, as shown in FIG. 5(d), a silicon nitride film 18 is formed and thereon an interlayer insulating film 19 is formed.
In such steps of forming a copper interconnection, it is essential to remove copper oxide which is formed on the copper surface so that the electrical resistance may be prevented from increasing. While copper oxide is removed with carboxylic acid in the above method, other methods such as a method by a plasma treatment with a reducing gas are also known. For example, in a method described in xe2x80x9cTDDB Improvement in Cu Metallization under Bias Stressxe2x80x9d by J. Noguchi et al. (IEEE 38th Annual International Reliability Physics Symposium, San Jose, Calif. 2000, pp. 339-343), a plasma treatment with a hydrogen or ammonia gas is carried out to achieve the reduction of CuO which is formed on the surface of the copper interconnection to Cu, along with the formation of a Cu layer thereon. Moreover, it is described therein that once CuN is formed, this may function as a protective film, and when a copper-diffusion prevention film of SiN or the like is grown thereon, the CuN layer can suppress the formation of the copper silicide layer in the copper interconnection and, therefore, can restrain the increase in electrical resistance.
However, conventional techniques described above have the following problems.
In a method comprising the step of removing a copper oxide film with carboxylic acid, after the cleaning to remove the copper oxide film is carried out, the wafer is taken out from the cleaning equipment and transferred for the step of growing the films. During the transfer, the wafer may be exposed to the air so that the copper surface therein may be reoxidized, leading to a problem of the increase in electrical resistance and the decrease in adhesion between the copper interconnection and the copper-diffusion prevention film formed thereon.
Meanwhile, although a method with a reducing plasma treatment can control the increase in resistance in a certain degree, the method brings about another problem of the decrease in interconnection lifetime. In fact, it is the present inventors who first confirmed, through experiments, that a reducing plasma treatment may lower the interconnection lifetime, due to the electromigration or the like, and give rise to a variation in resistance. To remove the copper oxide film thoroughly by the plasma treatment, it is necessary to employ considerably rigorous conditions for the plasma treatment and, as a result, the copper surface becomes rugged. Furthermore, since the nitridation to form CuN proceeds with copper oxide still partially remaining on the copper surface, the film thickness of the CuN becomes non-uniform and, herewith, the film thickness of a copper silicide layer that is to be formed in the copper interconnection becomes also non-uniform. This presumably causes a lowering of the interconnection lifetime and produces variation in resistance.
Further, in the method using the reducing plasma treatment, there are occasions where the film thickness of the copper-diffusion prevention film becomes non-uniform, owing to the unevenness of the underlying layer surface. This necessitates, in the later step of hole etching to form an interconnection connecting plug, to perform overetching further more so as to remove that copper-diffusion prevention film so that the degradation of the copper interconnection surface may be brought about by the plasma exposure.
In light of the above problems, an object of the present invention is to provide a manufacturing method of a semiconductor device which can improve the interconnection lifetime and the variation in resistance of the copper interconnection, while controlling the increase in resistance thereof, and, in addition, can raise the manufacturing stability.
The present invention provides a method of manufacturing a semiconductor device; which comprises the steps of:
forming a copper-containing film on a semiconductor substrate;
removing, with a cleaning agent, a copper oxide on a surface of said copper-containing film;
applying a nitriding treatment to the surface of said copper-containing film from which the copper oxide has been removed; and
forming a copper-diffusion prevention film comprising a silicon on said copper-containing film which has been subjected to the nitriding treatment.
Further, the present invention provides a method of manufacturing a semiconductor device; which comprises the steps of:
forming a copper-containing film on a semiconductor substrate;
removing a copper oxide on a surface of said copper-containing film;
applying an anticorrosive treatment to the surface of the copper-containing film, with an anticorrosive-containing solution being used;
carrying out a heating treatment to detach the anticorrosive which is adhered onto the surface of the copper-containing film and, subsequently, applying a nitriding treatment to the surface of said copper-containing film; and
forming a copper-diffusion prevention film comprising a silicon on said copper-containing film which has been subjected to the nitriding treatment.
Further, the present invention provides a method of manufacturing a semiconductor device; which comprises the steps of:
forming a copper-containing film on a semiconductor substrate; applying a nitriding treatment to the surface of said copper-containing film without allowing the semiconductor substrate to be exposed to an oxygen-containing atmosphere; and
forming a copper-diffusion prevention film comprising a silicon on said copper-containing film which has been subjected to the nitriding treatment.
In the afore-mentioned manufacturing methods, a nitriding treatment is applied to the surface of a copper-containing film, after copper oxide which is present on the surface of the copper-containing film is removed with a cleaning agent. Or a nitriding treatment is applied to the surface of a copper-containing film without allowing a semiconductor substrate to be exposed to an oxygen-containing atmosphere. In the method described in the BACKGROUND, wherein a copper oxide film is removed by a plasma treatment with a reducing gas, it is necessary to conduct the plasma treatment under somewhat rigorous conditions. For instance, in order to remove copper oxide, the plasma atmosphere is required to have a high reducing capability. This makes the surface of the copper-containing film rugged, causing the increase in interconnection resistance and contact resistance. Contrary to this, the plasma treatment in the present invention can be carried out under milder conditions, because the treatment does not aim at removing copper oxide.
Further, in the afore-mentioned conventional techniques, even if the treatment is conducted in a plasma atmosphere with a high reducing capability, a copper oxide film cannot help remaining in part. As against this, in the present invention, since the nitriding treatment is applied to a clean copper surface where no copper oxide film remains, the film thickness and the film quality of a CuN film which is formed by the nitriding treatment can be made uniform and, herewith, the film thickness of a copper silicide layer to be formed in the copper interconnection becomes uniform. As a result, the following effects can be attained.
First, the increase in electrical resistance which may be brought about by oxidation of the copper-containing film surface can be suppressed. In the afore-mentioned manufacturing methods, a protective film made of CuN is homogeneously formed to an uniform thickness over the copper-containing film so that a clean copper-containing metal surface where no copper oxide film is formed is directly covered with the protective film. This protects copper from oxidation with effect in the subsequent steps, and prevents the electrical resistance from increasing.
Secondly, the interconnection lifetime is lengthened. In the afore-mentioned manufacturing methods, CuN is formed, while the nitriding treatment is being applied to the surface of the copper-containing film, and once a copper-diffusion prevention film comprising silicon is formed, this CuN restrains silicon from diffusing into the copper-containing film. However, CuN does not cut off the silicon diffusion completely, and a small amount of silicon passes through CuN and reaches inside of the copper-containing film to form a thin copper silicide layer in the vicinity of the surface of the copper-containing film. As described above, the protective film made of CuN is homogeneously formed to a uniform thickness so that the silicide layer formed thereunder is a thin layer, homogeneous and having a uniform thickness. The formation of such a silicide layer is considered to be the cause for lengthening of the interconnection lifetime. A silicide layer of this sort can be also formed by the step of forming a silicon nitride film 18, in the method described in the BACKGROUND, referring to FIG. 5. However, because silicon nitride, in this instance, is deposited without a copper nitride layer being formed, silicon that is the very constituting material for silicon nitride diffuses into the copper interconnection, excessively, and a thick silicide layer is formed, causing a problem of the increase in interconnection resistance and contact resistance. Meanwhile, in the afore-mentioned method with a reducing plasma treatment, the formation of a silicide layer itself is considered to be suppressed. Unlike these conventional techniques, in the present invention, because a CuN layer, capable to restrain silicon diffusion appropriately, is formed, a silicide layer can be formed homogeneously and uniformly to a thin film thickness. This enables both objects, an improvement of the interconnection lifetime and a lowering of the electrical resistance, to be achieved together.
Thirdly, because the copper-diffusion prevention film can be formed homogeneously and with its film thickness well under control, the degradation of the copper-containing film in the subsequent steps can be prevented from occurring. For instance, when the present invention is applied to a method of forming a copper interconnection, after copper interconnection made of a copper-containing film is formed, an interconnection connecting plug is to be formed thereon. In the step of hole etching, thereat, it is required to remove the copper-diffusion prevention film and expose the copper interconnection. In order to remove the copper-diffusion prevention film lying in a plurality of holes for sure, it is essential to make a certain amount of overetching. Nevertheless, in the present invention, as the copper-diffusion prevention film can be formed homogeneously and with its film thickness well under control, the film thickness for the copper-diffusion prevention film itself can be made thinner than the conventional one, and, as a result, the amount of overetching can be well reduced. Doing this, the alteration of the resist form can be lessened and the linewidth accuracy of the fabricated form, heightened. Further, the thickness of the resist can be reduced so that more minute fabrication thereof can be made. In addition, the amount of deposits generated after etching may drop, and besides shavings and damages of the underlying copper interconnection due to overetching can be reduced. Further, as the film thickness of the copper-diffusion prevention film can be set thin, parasitic capacitances between horizontally adjacent interconnections and within the interconnection along the direction of the substrate thickness can be reduced. As a result, cross talk between interconnections can be suppressed.
In the afore-mentioned manufacturing methods of a semiconductor device, the nitriding treatment of the copper-containing film surface can be effected by a plasma treatment using a source gas comprising a nitrogen element. Further, following the step of removing copper oxide, and prior to the step of applying a nitriding treatment to the surface of a copper-containing film, the step of applying an anticorrosive treatment to the surface of the copper-containing film with an anticorrosive-containing solution may be carried out. Further, after the step of applying the anticorrosive treatment to the surface of the copper-containing film, the step of a heating treatment to detach the anticorrosive which is adhered onto the surface of the copper-containing film and, subsequently, the step of applying a nitriding treatment to the surface of the copper-containing film may be carried out. Hereat, if the afore-mentioned heating treatment is carried out in a vacuum and, thereafter, keeping the vacuum as it is, the step of applying the nitriding treatment to the surface of the copper-containing film is performed, the nitriding treatment can be applied to the surface of the copper-containing film which is in a clean state, the film thickness and quality for the copper nitride layer and copper silicide layer can be advantageously made more uniform.
As set forth above, the present invention can make the film thickness and the film quality of CuN that is formed by the nitriding treatment uniform and, herewith, can form a copper silicide layer to an uniform thickness in the copper interconnection. Consequently, the present invention can improve the interconnection lifetime, while preventing the resistance of a copper-containing film from increasing. Furthermore, because the present invention can form a copper-diffusion prevention film homogeneously with a film thickness well under control, it is possible to prevent the degradation of the copper containing film from occurring in the subsequent steps.